Inadequate deep sleep can be the quiet culprit of daytime fatigue or performance issues. During deep sleep, the body undergoes many types of repair and regeneration, making it vital to our sense of waking up refreshed. As a result, subtle and seemingly minor habits can interfere with your deep sleep and sabotage your mood and energy levels.

In this article, we examine the purpose of deep sleep, warning signs you may need more than you're getting, and guidelines for how you can increase your deep sleep. Many people find that even after covering the basics of sleep hygiene—like avoiding afternoon coffee or exercising regularly—their sleep still isn't as refreshing as it could be. 

This article will help you optimize the quality of your sleep while avoiding easy-to-overlook habits taking a silent toll on your daytime energy levels.

Deep sleep: A time of restoration

Deep sleep is technically called slow-wave sleep because electrical activity in the brain slows dramatically [1]. This puts the body into a state of physical paralysis, where our breathing, heart rate, and blood pressure reach their lowest points of the night. 

With all but our critical functions offline during this time, deep sleep is a period devoted to regeneration, making it the foundation not only of our health but our performance [2].

What makes deep sleep different from other sleep stages?

There are two types of sleep: rapid eye movement (REM) and non-REM sleep. Deep sleep is one of three stages of non-REM. Researchers broadly link non-REM sleep with physical recovery, while REM sleep is more prominently associated with emotional processing (though there is overlap between the two). 

Experts sometimes call REM "paradoxical sleep" [3] because our brains closely resemble their waking states: breathing becomes irregular, heart rate and blood pressure increase, and we dream (though it’s possible to dream in non-REM sleep too) [4].

Because we're most in need of recovery after being awake all day, pockets of deep sleep are typically concentrated earlier in the night, with lighter stages happening closer to morning. Each night, we cycle through three stages of non-REM, followed by one stage of REM sleep. This pattern repeats an average of four to six times throughout the night.

Why deep sleep is the foundation of high performance 

Scientific research into deep sleep has demonstrated its vast and multi-faceted roles in our health. It's essential for processes as diverse as immune and hormone regulation, mood, and memory [2].

Deep sleep is critical for many aspects of our daytime performance, including (but not limited to):

Consolidating memories 

During deep sleep, the brain consolidates memories and skills we've learned throughout the day into a long-lasting form [5]. While memory consolidation also occurs in REM sleep, studies have shown deep sleep supports declarative memory (recalling information) and procedural memory (learning new skills) [6]. 

With this and other roles deep sleep plays in our cognitive function, issues with deep sleep can manifest in problems with attention and alertness or recalling recently learned information. 

Recovery after exercise

Deep sleep is essential for building muscle in response to exercise. During deep sleep, the pituitary glands release high amounts of human growth hormone, repairing muscles and tissue and replenishing energy stores, leading to muscle development and other gains that occur in response to exercise [7]. 

Regulating appetite

Sleep quality influences appetite in two ways: according to research published in Nature Communications, insufficient sleep can trigger cravings for unhealthy food. It can also inhibit impulse control, which ordinarily prevents overeating [8].

Sleep deprivation impairs two appetite-regulating hormones, ghrelin, which stimulates appetite, and leptin, which reduces appetite. Without proper sleep, ghrelin spikes while leptin drops, intensifying hunger, and interfering with satiation cues meant to let you know when it's time to stop eating.

How to increase your deep sleep: Honor your body's love for rhythm

We could reduce all conversations about sleep quality to one sentence: Stabilize your circadian rhythm. We share our circadian rhythms—the 24-cycles governing our sleep-and-wake patterns, energy metabolism, and appetite—with other living things. 

Interestingly, every cell in the body has its own circadian clock [9]. When you wake up, eat, exercise, and go to sleep at roughly the same time each day, you bring all of these clocks into harmony, which is central to high performance.

By focusing on your circadian rhythm, you have a much higher likelihood of addressing the root causes of your sleep quality issues. By contrast, melatonin or other sleep aids can be useful in the short term, but they only offer superficial support, allowing the underlying problems driving your sleep issues to continue. 

1. Start your morning with sunlight exposure. 

Early morning sunlight issues a signal through the ganglion cells in your eyes, which lets your brain know the time of day [10]. This stimulates the release of peptides that serve as wake-up signals to the body. Early morning sunlight also interacts with the melanopsin cells in the retinas. This sets a timer that triggers the release of the sleep-inducing hormone melatonin 12 to 14 hours later [11].

Getting early morning sunlight will help your circadian rhythm more closely align with the sunrise and sunset, helping you naturally wake up and feel sleepy at the same time each day. By bringing regularity into your sleep habits, you’ll be less likely to struggle to fall asleep at night and less prone to middle-of-the-night wake-up calls. As a side benefit, the early morning sun can also help you train yourself to wake up earlier.

Get outside as soon after sunrise as you can. Even if it's cloudy, simply being outside (without sunglasses) will do the trick. Remember your location and the time of year will influence how much time you need to spend outside. If you're close to the equator, and it's summer, you might only need ten minutes or less. Conversely, in the winter, consider increasing your time outside to 30 minutes or longer.

If you consistently get early morning sun exposure, you'll also naturally adjust your wake-up time to align with the changing seasons. This habit can help ensure you're getting enough light exposure in the winter months. Adequate sunlight exposure can also mitigate winter fatigue, or the tendency to feel more tired during the winter months. While winter fatigue occurs for most people, it’s more disruptive to your focus and overall energy levels when you try to bring your spring, summer, and fall sleep-and-wake-up habits into the months with less sunlight.

2. Avoid late-night meals

The timing of your meals can also influence the quality of your sleep. When you eat, your body interprets it as a sign it’s time to process and digest, not wind down and fall asleep.

A study published in the Journal of Clinical Sleep Medicine documented the adverse effects of late-night eating [11]. The researchers studied the relationship between food intake and sleep patterns among healthy men and women between 19 and 45. The participants kept food diaries related to the foods they ate and when.

They found eating shortly before bedtime impacted many dimensions of sleep, with women being more sensitive to these effects. The participants had disruptions in...

• Sleep efficiency (the percentage of time spent asleep while in bed)
• Sleep latency (the amount of time to fall asleep)
• Sleep continuity (the likelihood of waking after falling asleep)

While this study was preliminary, it’s well known that digestion runs smoothest when you’re active and it’s daytime. As a result, eating when the body expects rest can disrupt your circadian rhythm, and by extension, your metabolism. 

Eating your meals at roughly the same time every day will support your circadian rhythm. The exact time you should plan to stop eating will depend on your metabolism, but two to four hours is a good baseline to aim for. Generally, the larger the meal, the longer you should wait before going to bed.

3. Time your exercise according to your chronotype. 

For many years, researchers urged people to avoid exercise at night, because of the stress it puts on the body. But recent studies have painted a more complex picture: individual differences can determine the degree to which exercise timing influences sleep quality.

A study published in Chronobiology International evaluated the ways exercise timing influenced the sleep of healthy, young adult male soccer players [12]. They found the participants' chronotypes strongly influenced whether late-night exercise interfered with their sleep quality. A chronotype is your natural inclination to wake and sleep at specific times (in casual conversation, people often use the terms  "night owl" or "early bird" to describe it).

In this case, early rising players had worsened sleep quality when they exercised in the evening. By contrast, those naturally inclined to stay up later could exercise late in the day without interrupting their sleep.

To learn about your sleep chronotype, we'd recommend taking Dr. Michael Breus' chronotype quiz, which can help you figure out whether late-night exercise could interfere with your deep sleep. 

Also, the following principles related to the sleep-exercise connection are worth keeping in mind.

• According to a recent randomized controlled trial, 150 minutes of moderate-to-vigorous exercise per week (or about 30 minutes per day) is the minimum level of activity you need for high-quality sleep [13].
• If you wake up in the middle of the night, mild aerobic exercise (walking) or resistance exercise (weight training) in the early evening may help. Lighter forms of exercise bring stress relief without raising body temperature enough to affect sleep. 
• In most cases, avoid exercise at least 90 minutes before bed [14]. If you have insomnia, studies suggest it’s best to do only light-to-moderate exercise four hours before bed [15].

4. Speak your body's language: Talk your nervous system into better sleep

There's a feedback loop between your autonomic nervous system (ANS) and your sleep. Being chronically stressed can make it physiologically harder for you to get deep sleep, while a lack of deep sleep can amplify your existing stress, further impairing your nervous system's resilience. (Note: If you're not familiar with the ANS, read our guide to the autonomic nervous system).

It sounds dire, but you can untangle this knot naturally and without high amounts of effort. Sending your nervous system a "signal of safety" can stimulate your parasympathetic (rest-and-digest) nervous system, breaking the cycle of stress and calming your body.

There are many ways to do this, but focusing on your breath is the best option for calming down for sleep: you can do it lying in bed (without a list of complicated steps) while feeling a difference in minutes.

The physiological sigh

This is a breathing pattern and a natural reflex we share with other animals. It was discovered in the 1930s to happen automatically when we enter sleep, or when we cry or feel claustrophobic. 

Neuroscientists Dr. Andrew Huberman and Dr. Jack Feldman popularized it as an exercise to quickly lower stress. It’s especially useful for moments when you don’t have time for a more intensive meditation or breathing practice.

To do the physiological sigh:

• Take two quick inhales through your nose
• Follow these inhales with one, long, controlled exhale through the mouth.
• Repeat as desired.

As explained by Dr. Andrew Huberman, our lungs are filled with millions of sacs called alveoli. Under stress, these sacs collapse, and carbon dioxide (CO2) builds up in the body. This can cause jitters and other sensations we associate with stress.

By inhaling through the nose twice, you reinflate any collapsed sacs, making your exhale more effective at dispelling excess CO2, exerting a calming effect.

The Apollo wearable

The Apollo™ wearable serves as another low-effort tool you can use to send your nervous system a signal of safety. The device sends patterns of vibrations (or modes) clinically shown to improve parasympathetic activity under stress, as measured by heart rate variability (HRV), a biomarker for the body’s ability to recover from stress.

We've specifically explored the Apollo wearable's impact on sleep quality within our ongoing, remote observation clinical trial [16]. Evaluating the sleep quality and cardiovascular metrics of 500 Apollo wearable users who also use the Oura ring, participants who used the Apollo wearable for at least 3 hours per day, five days a week had the most significant gains in their deep sleep, REM sleep, total sleep, resting heart rate, and HRV.

The study participants experienced (on average):

• 19% average increase in deep sleep
• 14% average increase in REM sleep 
• Up to 30 more minutes of sleep a night
• 11% average increase in HRV
• 4% average decrease in resting heart rate

The Apollo wearable's scheduling feature can be especially useful for improving your sleep quality. The scheduling feature was designed to help you build rhythms into your daily life. It allows you to create a customized schedule so the Apollo wearable’s modes change automatically at desired points throughout your day, setting the foundation for a stable circadian rhythm.

Over time, you’ll train your body to automatically enter states conducive to your schedule, so getting relaxed before bed or fired up before a run won’t involve as much friction or active planning. For more on this, read our article, how the Apollo Neuro™ team uses scheduling.

5. Measure trends in your HRV

Heart rate variability (HRV) is a biomarker of nervous system resilience. A high HRV suggests it can easily adapt to changing demands of the environment. A low HRV indicates you’re not recovering well from stress. Low HRV can increase your chances of developing insomnia, anxiety-related disorders, and other conditions [17].

While the Apollo wearable improves your HRV, many devices log trends in your HRV, which you can use to identify diet and lifestyle patterns impacting your sleep quality. 

There are two types of HRV devices. Passive devices monitor past HRV trends, while active devices monitor present, real-time trends. The second type can help you identify links between your habits and your HRV. Some of these devices include (not affiliate links)...

• Lief Therapeutics
• HeartMath Inner Balance
• Hanu Health

By tracking long-term trends in your HRV during sleep or throughout the day, you get direct insight into how specific diet and lifestyle choices are influencing your nervous system, and by extension, the quality of your sleep. Finding the motivation to break bad habits and form new ones becomes much easier when you can spot direct connections between what you do, what you consume, and your HRV.

6. Let there be light (at the right time). 

Most people have heard warnings about using blue light-containing screens after dark. The issue isn't so much about blue light itself, but the timing of the exposure. 

When you view blue light after dark, even a short window of exposure can suppress the sleep-regulating hormone, melatonin. Blue light exposure at the wrong times can interfere with everything from hormone secretion to heart rate to body temperature [18]. 

To prevent light from interfering with your sleep, try lighting your space with candles an hour before bed. This can not only help you create a soothing atmosphere, but it can also help you carry on with reading, meditating, or other relaxing activities without light disturbances. If that doesn’t seem like enough, try installing red light bulbs, which won’t interfere with your circadian rhythm at night [19]

8. Warm up to cool down: The delight (and the importance) of evening baths

Our body temperature plays a key role in regulating our sleep timing and duration, and it's lowest during sleep. 

By taking a warm bath or shower an hour or two before bed, you will aid in balancing your circadian rhythm and improve your likelihood of getting restorative sleep. Warm baths prepare you for sleep because they send blood toward the surface of the body and away from the core, resulting in an overall drop in body temperature.

A study published in Sleep Medicine Reviews reviewed 5,000 studies on bathing's effects on sleep. They discovered baths or showers between 104 and 109 degrees F for 10 minutes significantly improved the participants’ sleep efficiency, or the time spent asleep while in bed [20].

Another study had women over 60 with insomnia between 60 and 72 take a bath in hot (104 degrees F) and lukewarm (99.5 degrees F) baths 1.5 hours before bedtime. Those who took hot baths had significantly improved sleep continuity and deep sleep compared to those who took lukewarm baths [21].

9. Hypnotize your way into a deep, restorative sleep

Hypnotherapy has a vast literature behind it, with studies showing its promise as a side-effect-free tool helpful for anxiety [22], chronic pain [23], and many other uses. Researchers have specifically explored hypnosis as a strategy for alleviating sleep disorders and improving deep sleep in particular.

For example, a study published in the journal Sleep studied brain activity among 70 healthy females who listened to hypnotic suggestions before taking a 90-minute nap. The hypnotic suggestion to "sleep deeper" led to the participants having an 81% increase in deep sleep, along with a 67% decrease in their time spent awake [24]. 

Though this study took place during a 90-minute, daytime nap (rather than at night), their approach successfully increased the amount and duration of the participants' deep sleep.

While visiting a clinical hypnotherapist would be the best option, if it isn't feasible, preliminary evidence suggests self-hypnosis, in the form of apps or audio recordings, can be helpful for people having sleep, fatigue, or mood issues. 

When optimizing your deep sleep, remember the 80/20 principle

If you've had trouble getting high-quality sleep for a long time, most of the effort in changing your sleep habits will come at the very beginning. As the Pareto principle (also known as the 80/20 rule) states, 80% of your results come from 20% of your efforts.

Your 20% effort will likely happen the first day you get outside earlier than usual, or the first few times you decide against eating after dark. But after a few days, your body will naturally adjust, and these habits will become automatic. Sleep will more readily feel refreshing and easier to get without the same degrees of effort.

To the busiest among us, sleep can seem like a relatively dull endeavor. But the average person spends about 229,961 hours (or one-third) of his or her life asleep! Don't waste that time regretting your hesitancy to get a new pillow or stressing about why you always wake up at exactly 2:55 a.m. Every effort you devote to improving your sleep will compound in the sense of feeling energized, balanced, and mentally sharp during your waking hours.

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